Speedometer



C. G. SMITH.

SPEEDOMETER.

APPUCATION man Aue.22. 1919.

v 1,384,809. Patented July 19,1921.

WVitnes's nl/entar UNITED STATES PATENT OFFICE,

CHARLES e. sMITH, or CAMBRIDGE, MASSACHUSETTS, AssIG voR j 'MAGGILL, or CAMBRIDGE, MASSACHUSETTS T CHARLES r.

SPEEDOMETER.

To all whom it may concern:

Be it known that I, CHARLEs G. S ITH, a citizen of the United States, residing at Cambridge, in'the county of Middl'esex and- State of Massachusetts, have invented cer- 1 tain new and useful lmprovements in p'eed- 'ometers; and I do-hereby declare the followingto be a full, clear, and exact'desoription ofthe invention, such as will enable others skilled in the art to which it appertams to make and use the same. The present invention relates to speed 'ometers and more particularly to speedometers ofthe'type in which a torque is se't up through the rotation of a member within a viscous liquid.

' general type in which the inner rotating Patent No. 1,271,092, granted to Charles G. Smith, illustrates a speedometer of thls member is connected to the usual drive shaft through. a magnetic clutch which permits of hermetically sealing the containing member in which the viscous fluid is received w1th all of the advantages attendant thereon.

' the construction is simplified and the accuracy of speed indication is increased. To

this end one feature of the invention contemplates the provision of a fluid containing member connected directly to the usual drive shaft to rotate therewith, an inner member received within the fluid containing member and adaptedto be rotatedthereby through the viscosity of the liquid in the containing member, and an outer indicating member normally restrained against rotary movener member do not rotate with the drive shaft but are normally stationary at any given speed of rotation,.the position of the members depending upon the speed at any given time. This construction, in addition to its simplicity, has the advantage that the indicating cup and magnet ma be made 7 light in weight to respond instant y to variations in position of the inner member, yet

Specification of Letters Patent. Patented y 1921 Application filed. August 22, 1919. Serial No. 319,289.

vibrations or rapid fluctuations in the speed of the drive shaft are not transmitted to the indicating member. This is due partly to the fact that the inertia of the inner member tends to maintain it in the same position and partly to the design of the instrument by which a relatively thick copper screen is interposed between the magnet and the inner member so that any movement in the magnet immedlately produces eddy currents in the copper screen which react to prevent such a movement. Due to these factors the indication afforded by the present instrument is remarkably steady and free from fluctuations of the indicating dial.

' The drawing illustrates a partially diag'rammatic view of an instrument embodying the several features of the'invention.

' Inthe illustrated embodiment of the invention shown in the drawing the usual drive shaft is indicated at 10. This shaft is provided at'the upper portion with a head 12 reduced in diameter at its upper portion, as

indicated at 13, andcooperating with a shell- 14 to provide a closed fluid containing member. The shell 14 is conveniently made as a steel stamping in the form of a cup with the lower edge rolled into a peripheral groove 16 formed adjacent the base of the head, as shown in the drawing. This construction provides an inverted cup-shaped space in which the liquid is contained. The head 10 is also provided with an axial recess 17 communicatingwith the liquid space at the top andwith a branch passage 18 which connects the recess 17 and the bottom of the annular liquid space to prevent any possibility'of the formation of air pockets. An inner rotary member 20 in the form of an inverted cup is received within the space formed by the head 12 and shell 14; and is mounted for rotation upon a spindle 21 which is positioned in alinement with the axis of rotation of the drive shaft and head 12 and has its upper and lower ends journaled in bearings 23 and 24 formed, respectively, in the shell 14 and the bottom of the recess 17. 'The inner member is formed of soft iron or other magnetic material and may be constructed by interposing between two cups of thin non-magnetic material a thin strip of iron bent into cylindrical form. This provides a construction having a or: other material.-

. mercury. This liquid is practically unaffectedby temperature and owing to its character exerts a relatively large torque upon theginner member at the. different speeds of thedrive shaft, I

I The ind cating me ber comprises an 1nverted clip of celluloidor other material having a permanent steel magnet 26 connected rigidly therewith. The magnet, as shown inthe drawings, extends downwardly from its connection with the indicating cup in close proximity to the shell Both themagn'et and indicating cup are mounted for rotationcoaxially with the head 12 and inher member and to this end asupporting spindle 21 is journaled at its upper and lower ends, respectively,

7 29 mounted in alinement with the bearings for the inner member. The lowerb'earing '29 is supported in a copper cup. which the spindle 27 normally tends to maintain v is secured rigidly to the frame of the inst/rip ment inany suitable manner not shown. This cup is relatively. thickand heavy and in ad-' ditionto providing a rigidb'earing' for the magnet .and indicating members serves to dampen the movements of the magnet and indicating member due to eddy currents which are set up in the relatively thick sheet of copper. A spiral spring 32, connected to the magnet and indicatingmeinberin a zero position and to restrain the'indicating mem-- ber against movement with the inner member20.

In the operation of the instrument the fluid containing member consisting of the head 12 and the shell 14 is rotated with the 7 drive shaft, exertinga' torque upon the 'inher member 20 through the mercury or other liquid contained therein. This drag exerted upon the inner member tends to rotate the latter with the drive shaft. The inner member, however, is restrained against such movement by being magnetically} clutched to the indicating member 25, so that in' op-' eration the innermember 2i) and'the indicating member 25 move to a position deter mined by the speed of the drive shaft and remain stationary in this position so long as the speed remains unchanged. Owing to the inertia ofthe' member 20 and the eddy currents set up in the copper shield 30, vi-

is claimed is in bearings 28' and her member.

brations and sudden fluctuations of speed in the drive shaft are not transmitted to the indicating member. This construction provides an exceedingly simple and efiicient' mechanism for indicating at all times the speed of the drive shaft.

While it is preferred to employ the specific construction and arrangement of parts showi'i and described, it will be understood thatrthis construction and arrangement is not essential except so far as specified in the claims, and may be changed or modified without departing from the broader features of the invention. r

The invention having been described, what 7 1. A speedometer comprising a 7 drive shaft, a rotary fluid containing member connected thereto, an inner member of magnetic material journaled coaxially within the fluid containing member, anindicating cup jjournaled for rotary movement coaxially with the inner member, and. a magnet associated with the indicating member to clutchgthe indicating member to the inner member.

2. A speedometer comprising a rotary,

fluid containing head, a cup'recei'ved within the head and j ournale'd for rotation coaxially with the head, an indicatingv member, means for normally restraining the indicating member against rotary movement,,and a magnet connected I to the indicating member and adapted to clutch the indicating member to the innerrotary member. V

3. A speedometer comprising a; rotary head having a fluid chamber "inthe form of an inverted cup with-an axial fluid passage communicating with {the chamber a cupshaped member received within the fluid chamber for rotary'movement about the axis' of rotation of the head, an indicating member journaled for rotation aboutfthesame axis, and a magnet connectingthe inner cupshaped member and indicating member to cause the two members 'to move: synchronously. Y Y

4. A speedometercomprising a} sealed fluid containing head rotating with the drive shaft, an inner member loosely .j ourna'led for rotary movement about the axis of rotation of the head and composed. of mag.- netic material, an indicatingmemb'er jour-- naled above the head for"rotary"move ment about the same axis, a magnet connectedto the indicating member, and a copper screen interposed between the magnet and theine 5. A speedometer 'comp'rising'a rotary fluid containing head having a reduced upperp'ortion, a metal shell: in theform of an inverted cup received over the. head andhav-x member received within the chamber and loosely journaled for rotation about the axis of rotation of the head, and an indicating member magnetically clutched to move with 5 the inner member.

6. A speedometer comprising a rotary head having a fluid chamber, liquid mercury received within the chamber, a member received within the chamber adapted for r0- tation about the same axis as the head, and an indicating member journaled for rotation about the same axis and magnetically clutched to the inner member.

CHARLES G. SMITH. 

